FFT add simple median filter

src/lib/mathlib/math/filter/MedianFilter.hpp

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+/****************************************************************************
+ *
+ *   Copyright (C) 2020 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/*
+ * @file MedianFilter.hpp
+ *
+ * @brief Implementation of a median filter with C qsort.
+ *
+ */
+
+#pragma once
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+namespace math
+{
+
+template<typename T, int WINDOW = 3>
+class MedianFilter
+{
+public:
+	static_assert(WINDOW >= 3, "MedianFilter window size must be >= 3");
+	static_assert(WINDOW % 2, "MedianFilter window size must be odd"); // odd
+
+	MedianFilter() = default;
+
+	void insert(const T &sample)
+	{
+		_head = (_head + 1) % WINDOW;
+		_buffer[_head] = sample;
+	}
+
+	T median()
+	{
+		T sorted[WINDOW];
+		memcpy(sorted, _buffer, sizeof(_buffer));
+		qsort(&sorted, WINDOW, sizeof(T), cmp);
+
+		return sorted[WINDOW / 2];
+	}
+
+	T apply(const T &sample)
+	{
+		insert(sample);
+		return median();
+	}
+
+private:
+
+	static int cmp(const void *a, const void *b)
+	{
+		return (*(T *)a >= *(T *)b) ? 1 : -1;
+	}
+
+	T _buffer[WINDOW] {};
+	uint8_t _head{0};
+};
+
+} // namespace math

src/lib/mathlib/math/filter/MedianFilterTest.cpp

@@ -0,0 +1,93 @@
+/****************************************************************************
+ *
+ *   Copyright (C) 2020 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * Test code for the Median filter
+ * Run this test only using make tests TESTFILTER=MedianFilter
+ */
+
+#include <gtest/gtest.h>
+#include <matrix/matrix/math.hpp>
+#include <mathlib/mathlib.h>
+
+#include "MedianFilter.hpp"
+
+using namespace math;
+using matrix::Vector3f;
+
+class MedianFilterTest : public ::testing::Test
+{
+public:
+
+
+};
+
+TEST_F(MedianFilterTest, test3f_simple)
+{
+	MedianFilter<float, 3> median_filter3;
+
+	for (int i = 0; i < 3; i++) {
+		median_filter3.insert(i);
+	}
+
+	EXPECT_EQ(median_filter3.median(), 1); // 0, 1, 2
+}
+
+TEST_F(MedianFilterTest, test3f_100)
+{
+	MedianFilter<float, 3> median_filter3;
+
+	for (int i = 0; i < 100; i++) {
+		EXPECT_EQ(median_filter3.apply(i), max(0, i - 1));
+	}
+}
+
+TEST_F(MedianFilterTest, test5u_simple)
+{
+	MedianFilter<uint16_t, 5> median_filter5;
+
+	for (int i = 0; i < 5; i++) {
+		median_filter5.insert(i);
+	}
+
+	EXPECT_EQ(median_filter5.median(), 2); // 0, 1, 2, 4, 5
+}
+
+TEST_F(MedianFilterTest, test5i_100)
+{
+	MedianFilter<uint16_t, 5> median_filter5;
+
+	for (int i = 0; i < 100; i++) {
+		EXPECT_EQ(median_filter5.apply(i), max(0, i - 2));
+	}
+}